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Old 11th September 2017, 10:46 AM   #871
eduard is offline eduard  Netherlands
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Hello,
Tubes not connected yet.
Overkill surely but if it can improve for a few euros it will be beneficial.
5687 will be improved a little not as much as a what for sure.
But changing into choke input for th lm350 was also a big improvement.
We will see .
Of course everybody here should switch to high efficiency drivers.
Greetings,
p.s Dht with mediocre speakers will still sound mediocre
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Old 24th September 2017, 04:51 PM   #872
eduard is offline eduard  Netherlands
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Hello,
Not sure yet But it seems switching to choke-put with the lm350 regulator was a bigger difference than switching from the lm350 to the coleman both with choke input.
I understand with a DHT changing in the heater supply will give bigger difference.
BUT the Coleman is cheap compared to a more regular heater supply.
Greetings, Eduard
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Old 24th September 2017, 08:48 PM   #873
Rod Coleman is offline Rod Coleman  United Kingdom
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New DHT heater
Changing from Cap-input to choke-input can reduce the noise coupling from this dc supply to other (more sensitive) parts of your system, like the DACs, or MC preamp stage - and that could give a better overall sound.

as Andy says, you're now in a good position to compare the range of useful DHTs for preamp duty - 4P1L is certainly a good start, and there's plenty of build guidance over at the 4P1L preamp thread.
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Old 25th September 2017, 02:20 AM   #874
Truetone is offline Truetone  Australia
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I am using a raw supply (845 Coleman reg) that consists of a 5A LT338 regulator board from Audiowinds 5AMP 1.5-32V Adjustable Voltage Regulator Module, LM338 | eBay

I put 100 Ohm across it to give a resistive load. It works fine but have thought about building a choke input passive supply. Any thoughts? Do I get the full benefit of the Coleman board this way? I was using the board to directly supply the filaments before.

I built a choke input supply for 4P1L Coleman boards on my filament bias preamp.
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Old 25th September 2017, 03:43 AM   #875
Truetone is offline Truetone  Australia
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One good thing about using a regulated raw supply is you can set the voltage for minimum and unvarying dissipation at the coleman board. I find this set up to stay cool, but it's not summer here yet! An easy way to mount the board to the chassis is to cut a small square section of aluminium and drill / tap one end and side.

Click the image to open in full size.

Last edited by Truetone; 25th September 2017 at 03:46 AM. Reason: image
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Old 25th September 2017, 04:39 AM   #876
eduard is offline eduard  Netherlands
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hello,
You will need a big choke like the Lundahl ll2733 with two coils in parallel to withstand the high current needed for the 845 and you will need another transformer for sure.
And i would install a bleeder resistor to take care of the minimum current needed to make it work as a choke input.
greetings, erduard
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Old 3rd October 2017, 08:20 AM   #877
Truetone is offline Truetone  Australia
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Any advice rgds the delay period for filament heating on 845? Does it damage the cathode if the B+ comes on first? eg as with a DH rectifier tube. I have always used a pre-heat sequence but no longer practical (for other reasons). Given that the high initial voltage is within components spec. Thanks.

Last edited by Truetone; 3rd October 2017 at 08:21 AM. Reason: proviso
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